1. Field of the Invention
This invention relates to foam delivery systems, and in particular to a foam generating nozzle assembly for use in such systems.
2. Description of the Prior Art
It is known in the prior art to employ expansive foam in fire fighting. Typically such foams are formed from water-soluble surfactants of the perfluorocarbon type which may be dispensed from a variety of different types of equipment, all well known in the art. One such typical material is known in the art as AFFF, see U.S. Pat. Nos. 3,258,423; 3,562,156 and 3,772,195, for example. Generically these materials are also known as FCS and HCS materials, e.g., fluorocarbon surfactants and hydrocarbon surfactants. Variations include those AFFF compositions which include a fluoro-chemical synergist known as F-amide and an FCS called F-AMPS, see for example U.S. Pat. Nos. 4,090,367 and 4,014,926. These foam producing materials are known to produce high-expansion foams which are known to spread over the surface in order to suppress vaporization of gasoline, which is the principal reason these materials were developed. Other patents which disclose similar materials are U.S. Pat. Nos. 4,442,018 and 4,770,794.
Foams from the above and other equivalent materials tend to be of small envelope or bubble size and flowable, the latter being one of the desirable qualities for use in fighting fires. Moreover, the foams may be formed relatively easily at the site of application by any number of different devices, all well known in the art. Portable units of various sizes as well as truck mounted units are commercially available for forming and dispensing various amounts of foamed material. For example, units are available which dispense from 2,000 to 15,000 or more cubic feet of foam per minute. Dispensing units include water reaction motors, electrically powered units, turbine units, compressed gas driven units and the like. Some of the dispensing equipment includes a tubular member which may be from two feet to ten feet in diameter, connected to the foam generator, and used to control the direction of foam discharge. The foam is discharged from the open end to the tubular member remote from the foam generator. The result is that an enormous amount of foam may be quickly dispensed from a relatively small unit in a relatively short time using a relatively small amount of water and foaming agent. Since the foam includes a surfactant, it tends to flow easily and spread quickly over the contact surfaces which it readily wets. Such foams may also be dispensed from high velocity nozzles and projected a relatively long distance and with sufficient accuracy to reach a designated target area.
Typically, the foams above described are sometimes referred to as expanded foams, having an expansion ratio of 50 to 1 to 1000 to 1. These types of foams do not have sufficient strength to remain in a three-dimensional shape, for example, a mound, for any significant length of time. The foams described, dispensed by known equipment and techniques, tend to have a relatively long life since collapse of the foam is due principally to evaporation of the water component of the foam. Thus in the absence of heat or flame, the foam tends to remain fairly stable for a relatively long period. However, it is also true that the foam tends to spread laterally rather quickly since this is one of the desirable features in its use as a fire fighting material.
It is also known in the prior art to use such foams in blast suppression e.g. to disrupt improvised explosive devices (IED's) specifically in U.S. Pat. No. 4,589,341, a blast suppression method is provided through the use of foams heretofore used in fire fighting and wherein the formed foam is confined in such a way as to control the continued propagation of the blast wave, thereby absorbing the compression wave in all radial directions or selectively absorbing the blast wave so that its continued propagation in any given direction is suppressed.
Class A foams are used for cellulose-based fires, and Class B foams are used to combat flammable liquid fires.
It is also known to generate foam by spraying a foamable liquid onto a perforated metal screen, while blowing air through the screen. See U.S. Pat. No. 3,723,340.
Also, a plurality of spaced horizontal sieves are employed in the foam dispenser nozzle disclosed in U.S. Pat. No. 5,064,103. The sieves have different sized openings, decreasing in size toward the discharge orifice.